The present invention is directed to antennas for use with ultrawideband (UWB) systems, particularly spiral type antennas. Spiral antennas have long been used as frequency independent, “dc-to-daylight” ultrawideband (UWB) antennas. By scaling the spiral geometry over an arbitrarily large range, a spiral antenna may be made sensitive to an arbitrarily large bandwidth.
More recently, there has been interest in ultrawideband antennas to meet the needs of commercial UWB systems compliant with the 3.1-to-10.6 GHz authorization by the Federal Communication Commission. More modern UWB antennas suitable for use with these commercial UWB systems differ from classical “dc-to-daylight” UWB in two important regards.
First, commercial UWB systems must meet a well-defined mask covering about a 3:1 range of frequencies. Unlike classical “dc-to-daylight” UWB antennas for which more bandwidth is always better, modern UWB antennas need just enough bandwidth to enable their corresponding system to meet the regulatory mask. Excessive bandwidth can be detrimental for modern UWB antennas because it opens the RF front end to out of band emitters and worse, makes it more difficult for an associated UWB system to meet the desired mask.
Second, commercial UWB systems should ideally use low dispersion antennas. Classical frequency independent antennas radiate low frequency signals from a large scale section and high frequency signals from a small scale section. This variation in the location of the effective source of radiation can cause dispersion. A dispersive antenna radiates a different signal with different frequency components and phase relationships in different directions. This dispersion can have serious negative impacts on the performance of a UWB system.
At the same time though, spiral antennas have certain characteristics that make them of value for the transmission and reception of UWB signals. Spiral antennas are relatively compact and also radiate and receive mixed or chiral polarization signals.
Thus, there is a need for a spiral antenna with an ultrawideband response but not so broadband as to make compliance with a regulatory mask difficult. There is a further need for a low dispersion spiral antenna.